1. Field of the Invention
The present invention relates generally to an image processor for reading an image on a frame of a microfilm using an image sensor, such as a CCD line sensor, and particularly to a method of and device for selectively detecting the image area to remove the unnecessary marginal portions surrounding the image area and to detect only the designated image area.
2. Related Art Statement
There is known a microfilm reader by which an image in a frame of a microfilm is read by an image sensor and the output signal is binarized while referring to a pre-set binary level to obtain image signals. Since each frame of the microfilm has marginal portions in which no image is present, these marginal portions are read by the image sensor together with the image area in each frame. As a result, black marginal portions surround the image area when the output signal are printed out.
In order to erase such black marginal portions, various approaches have been proposed. For example, addresses defining the image area in co-ordinates are input through a keyboard or the movable marks. However, such input operations are generally troublesome and time-consuming operations.
Another approach is to discriminate the image area from the marginal portions by referring to the level of the output image signals. However, such an approach involves the problem that blip marks or like marks are erroneously detected as though they constitute the portions of the image.